Method and apparatus for the treatment of molten metal

ABSTRACT

THE MOLTEN METAL TO BE TREATED IS MADE TO ASCEND FROM A COMPARTMENT IN A FIRST VERTICAL CONDUIT BY AN INJECTION OF GAS. FROM THE FIRST CONDUIT, THE METAL FLOWS THROUGH A SUBSTANTIALLY HORIZONTAL CONDUIT WHERE FARTHER GAS MAY BE INJECTED. THE TREATED METAL MAY RETURN TO THE COMPARTMENT IT COMES FROM OR TO ANOTHER VESSEL.

May 23, 1972 E, sp RE ET AL 3,664,652

MOb'lt N METAL.

METHUU AND APPARATUS FOR THE TRUA'I'MKEIN'F 0i 5 Sheetsheet l File-:1 Oct. 14, 1969 Fig. I I

LCT/E/V/VE JP/AE METHOD AND APPARATUS FOR THE TREATMENT OF MOL'IEN METAL Filed 001;. 14, 1969 May 23, 1972 5, 5pm: ETAL 5 Sheets-Sheet 2 f7/E/V/VE' JP/eE. 1 /15 @KE faint/7M 57 f flrrya May 23, 1972 $p|RE ET AL 3,564,652

METHOD AND APPARATUS FOR THE TREATMENT OF MOLTEN METAL Filed Oct. 14, 1969 5 Sheets-Sheet 3 May 23, 1972 SPlRE ETAL 3,664,652

METHOD AND APPARATUS FOR THE TREATMENT OF MOLTEN METAL Filed (Kit. 14, 1969 5 Sheets-Sheet 4 Awe/Wm 6v rJM May 23, 1972 E. SPIRE E AL 3,664,652

METHOD AND APPARATUS FOR THE TREATMENT OF MOIJTEN METAL Filed Oct. 14, 1969 5 Sheets-Sheet 5 fT/E/V/VE 5/ 065 P/EE/Qf Kmw/Ww :4 TTYJ United States Patent 9 p Int. Cl. czlc 7/00 US. Cl. 266-34 A 11 Claims ABSTRACT OF THE DISCLOSURE The molten metal to be treated is made to ascend from a compartment in a first vertical conduit by an injection of gas. From the first conduit, the metal flows through a substantially horizontal conduit where farther gas may be injected.

The treated metal may return to the compartment it comes from or to another vessel.

This invention relates to a process for the batch-wise or continuous treatment of molten metal.

It has been found that a particularly effective way of effecting a treatment of a molten metal is to pass an intimate mixture of gas or vapour and molten metal through a substantially vertical conduit, as part of a circulation path for the molten metal, and to subject the molten metal to one or more chemical or physical processes while in such circulation. It is possible to carry out this procedure in a relatively sturdy and inexpensive apparatus.

According to one aspect of this invention, there is provided a method of effecting a batch-wise or continuous treatment of a molten metal body, wherein said treatment is carried out while the molten metal body is located in a substantially vertical conduit, which conduit communicates at a lower part thereof with a chamber containing molten metal to be treated and is of substantially reduced cross-sectional area in relation to the cross-sectional area of the chamber, which method comprises injecting the molten metal while in said lower part of the conduit with a gas or vapour injected in a quantity sufficient to entrain the molten metal and convey it towards an upper part of the conduit where the molten metal is substantially at the ambient atmospheric pressure.

According to a second aspect of this invention, there is provided an apparatus for use in the treatment of molten metal, which apparatus comprises a substantially vertical conduit which communicates at a lower portion thereof with a chamber for containing, in use, a molten metal, and which is of substantially reduced cross-sectional area in relation to the cross-sectional area of the chamber, means for injection of gas or vapour into said lower portion to entrain and convey metal from said lower part to an upper part of said conduit where the metal will be at substantially atmospheric pressure, and means for allowing the metal so conveyed to leave said upper part of the conduit.

In a preferred embodiment of the invention, a second conduit is provided downstream of the upper part of the substantially vertical conduit, having an inlet in communication with the said conduit upper part and being horizontal or downwardly inclined at a small angle to the horizontal, at least over the major part of its length, which second conduit is provided at its downstream end Patented May 23, 1972 ICC with exit means, the gas or vapour injection means being capable of providing a quantity of gas or vapour at a sufiicient rate to allow the conveyed molten metal to enter the second conduit.

The gas or vapour may be injected into the lower portion of the first conduit through a porous, gas permeable, member. The dispersion of the gas into a multitude of very fine bubbles creates a thorough mixing of gas and metal, which displaces the metal upwards by hydrostatic pressure and into the second conduit, when present. It is also possible to use, as injection means, a nozzle or a perforated block.

The flow parameters in the apparatus of the invention are related in the case of treatment of liquid steel at 16 C., by the following equations:

In these equations, it has been assumed that the speed of ascent of the gas bubbles in the metal is equal to 1.5 m./ sec. In the equations:

V=speed of ascent of the metal, in meters per second;

f=height of expansion in meters, that is to say the additional height of metal in the single, or first, conduit above that of metal in the chamber, if, in the former case, the conduit is sufficiently high for the metal to remain therein;

h=height of the metal in the chamber in meters;

q=volume flow rate of gas injected into the conduit (first conduit) in m. /s.;

S cross-sectional area of the conduit (first conduit) in Q=rate of flow of metal in circulation in kg./s.;

p=ratio between the volume of gas and the volume of metal in the ascending column.

The coefficient 6.29 is equal to 1,873/2,9'8, the ratio of the absolute temperature of the steel to the normal absolute temperature of the gas.

The factor 7- 10 is the specific mass of the molten steel in kg./m. at 1,600 C.

g is the acceleration due to gravity (g.=9.81 m./s.

The method according to the invention is more effective in many cases and can be carried out more rapidly than when using ladles or furnaces through the bottom of which a gas is injected through one or more porous, gas permeable, members. The apparatus required can be constructed and used much more simply and is of much smaller bulk than the furnaces and ladles presently used for treatment by vacuum means and in known metallurgical installations wherein a gaseous, liquid or solid substance is injected in suspension in a gas. The capacity of the apparatus can vary greatly while remaining easy to use; for example, it can contain from several tens of kilograms up to metric tons or more. The metal can circulate therein in a closed circuit or pass through only once for a single treatment, depending on the par ticular requirements. The relatively small bulk makes it possible to collect easily any fumes which are produced.

Many different treatments of molten metal can be carried out employing the method according to the invention, in particular treatments which can be carried out as the metal flows during such treatments, including:

Deoxidation, dehydrogenation of ferrous or non-ferrous metal by injecting a reducing gas, an inert gas or both types of gas; the entraining gas may be sufiicient for this purpose;

Refining of pig iron by injection of oxygen allowing to tap, before complete refining, low-carbon pig iron or steel having a desired carbon content;

Nodulation of pig iron by adding a magnesium alloy or rare earth metal, for example, cerium;

Selective elimination of manganese, cobalt, etc. in the molten metals by injecting a halogen, such as chlorine, or, preferably, a halogen compound, for example CCI Addition, in the absence of air, of oxidisable com ponents of alloys, for example by mixing or by injecting volatile compounds of these elements; and

Purification of non-ferrous metals by injecting chlorine or compounds thereof, or other halogens or halogen compounds.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1 shows, in vertical section, a first embodiment of apparatus according to the invention;

FIG. 2 shows, in vertical section, a second embodiment of apparatus according to the invention;

FIG. 3 is a plan view of a third embodiment of apparatus according to the invention and FIG. 4 is a vertical section through the apparatus of FIG. 3 in a section taken on the plane IVIV of FIG. 3;

FIG. 5 is an horizontal section through a fourth embodiment of apparatus according to the invention taken along the plane VV of FIG. 6 which is a vertical section through the apparatus of FIG. 5 taken at the plane VI- VI of FIG. 5;

FIG. 7 shows, in vertical section, a fifth embodiment of apparatus according to the invention at the plane VII- VII of FIG. 9, FIG. 8 shows a vertical section through the apparatus of FIG. 7 taken on the plane VIIIVIII of FIG. 7, and FIG. 9 is a plan view in section through the apparatus of FIGS. 7 and 8 taken obliquely along the plane IX-IX of FIG. 8.

Referring now to the drawings, FIG. 1 shows a very simple form of apparatus suitable for use in batch-wise operation. The apparatus comprises a ladle 1 containing a metal 3 to be treated surmounted with a layer of slag 20. A partition 4 having a lower orifice 12 and an upper orifice 19 below the surface level of the molten metal is provided in the ladle to form with the wall of the ladle, an upwardly extending or substantially vertical conduit 8. A nozzle 21 for the injection of gas is provided, the gas causing the metal to flow in the direction represented by the arrows.

A porous, gas permeable: member 23 is optionally provided for a second injection of gas, such an injection promoting the upward movement of solid impurities in the metal bath. A cover 25 attached to the upper edge of the ladle can be swung over the conduit 8 to diminish heat losses and splashing. This cover can be so dimensioned as to cover the entire ladle. The ladle can be emptied by means of a stopper rod 50.

Referring now to FIG. 2, an apparatus is shown comprising a ladle 1 and a removable siphon 5 suspended by chains 7, 9 in molten metal 3 in the ladle. The siphon is made of sheet metal protected by refractory cement at the places which comes into contact with the molten metal. It comprises a vertical conduit 8 provided, towards its lower end, with a porous, gas permeable, sleeve 11 supplied with the gas through a tube 13, the duct 15 being incorporated in or formed in the wall of the conduit.

The injection of gas into the molten metal reduces the density thereof in the conduit and causes it to rise. An elbow 17 in the siphon enables the metal to fiow back into the ladle 1 sheltered from the ambient air and thus reduces splashing and heat losses. The molten metal may again be surmounted with a layer of slag in the same manner as shown in FIG. 1.

It is also possible for the siphon to be integral with the ladle in the manner shown subsequently in FIGS. 5 and 6.

Instead of returning the metal to the ladle from which it was taken it can be circulated by pouring.

Turning now to FIGS. 3 and 4 of the accompanying drawings, there is shown an apparatus comprising a first conduit and a second conduit through which molten metal passes successively. The apparatus comprises a ladle 2 containing molten metal which it is desired to treat before pouring it into another vessel. This ladle comprises an internal partition 4 which is extended, together with a lateral wall of the ladle, above the level thereof to form an elongated pouring spout 6.

The partition 4 forms a first conduit 8 with the lateral wall of the ladle. This conduit communicates with the main part of the ladle, the compartment 10, containing the metal to be treated and, if desired, a layer 20 of slag thereabove, through an orifice 12 situated at its lower portion. The lowermost portion of the conduit 8 is situated above a porous, gas permeable, member 14 through which a gas, supplied through a conduit 16, can be blown. This gas serves to reduce the density of the melt contained in the conduit 8 and to cause it to rise to a higher level than if no gas were blown in. The possible theoretical additional height to which the metal can rise has hereinbefore been designated by the letter 1. The orifice 12 is profiled in such a manner as to reduce head losses occurring at this region. Its cross-section depends on the cross-section of the conduit 8; it advantageously amounts to between 20% and of the latter cross-section.

The pouring spout 6 constitutes a second conduit. It is arranged down-stream of the first conduit, being connected to the upper portion thereof by an elbow 22. The second conduit comprises a horizontal portion 24 narrower than the first conduit, which extends downwardly and widens to form a chamber 26 which is provided with a pouring orifice 28 and a vent 30 which can be surmounted with a chimney (not shown). The shape of this second conduit can be varied, and it can, for example, be cylindrical, or the vent 30 can be dispensed with.

The presence of the second conduit increases the duration of the time during which the injected gases act on the molten metal. It allows one to inject further quantities of gas, which quantities can be greater than those blown into the lowermost portion of the first conduit. The narrowing 24 of the second conduit facilitates mixing of the contents thereof with an additional quantity of gas which can be injected into the second conduit, for example through nozzles or tuyeres 311, 32. This gas may have a chemical action or simply a degasifying action. The nozzles are above the surface level of the metal when there is no injection of gas at the base of the first conduit, and may be cooled by water without any risk of accident. Operation of the nozzles can be stopped at will during such absence of injection.

A liquid or a powder, for example magnesium or cerium alloy can be introduced into the second conduit through the nozzles 31 and 32 when one wishes to carry out modulation of the pig iron. In this case, the liquid or powder is carried along by a gas with which it does not react.

The base of the highest portion of the second conduit that is the base of the horizontal portion 24, is higher than the level to which the metal would rise if there were no gas injection in the first conduit. This prevents the contents of the compartment 10 from flowing spontaneously, when there is no such gas injection, until the surface level of molten metal has subsided below the base of the horizontal portion 24.

The first conduit 8 is relatively narrow so that the molten metal which passes therethrough is substantially thoroughly mixed with the gas introduced through the porous member 14.

The metal treated by the gas injected through the member 14 and through the nozzles 3-1, 32, if present, is poured out through the orifice 28 into a tapping ladle 34. The ladle 34 comprises a wall 36 which serves as a barrier against floating impurities and splashes from the orifice 28, and also an aperture with stopper rod 38 for supply of the melt to a mould 40. The mould shown can be replaced by a conventional ingot mould with a base plate or by a bottomless mould for continuous casting.

The contents of compartment 10 being covered by a protective layer of slag, and the ladle 34 and the mould 40 or ingot mould being in position, a gas, for example argon, is injected through the porous member 14. The gas causes the metal to rise in the conduit 8 and escapes through the vent 30 whilst the metal flows into the ladle 34 and thence into the mould 40 when the stopper rod is lifted. When the rate of injection of gas is no longer suflicient to make the metal rise to the level of the conduit 24, the ladle 2 can be inclined by rotating it on its trunnions 42, 44 in the direction of the arrow 46.

Referring now to FIGS. and 6 of the accompanying drawings, in which like reference numerals are given for the like parts shown in the apparatus of FIGS. 3 and 4, the apparatus differs from that shown in FIGS. 3 and 4 mainly in that the second conduit 24, 26 serves to recirculate the treated metal into the compartment 10. The end 48 of this conduit debouches below the layer of slag 20 in order to protect the metal from the action of the atmosphere. Complete treatment of the molten metal is effected with this ladle before pouring it into an ingot mould or any other mould. The metal can be poured into the mould simply by lifting a stopper rod 50, only the lower portion of which is shown in FIG. 6. The ladle can be tilted about tunnions 52, 54 if a stopper rod is not provided.

The positioning of the second conduit substantially entirely clear of the molten metal Will increase the working life thereof considerably and allows the use of cooled nozzles such as 31, 32 debouching thereinto.

The process according to the invention can also be carried out using a number of elements which may or may not be juxtaposed, and through which the metal passes successively.

Referring now to FIGS. 7, 8 and 9 of the accompanying drawings, there is shown an apparatus suitable for oncethrough treatments, in a similar manner to the apparatus shown in FIGS. 3 and 4. The apparatus comprises three compartments for the metal to be treated arranged in series and providing three first conduits and three second conduits. It is thus possible to carry out successive treatment by different gases readily, and to remove incompletely treated metal easily. The number of compartments and conduits can be varied according to requirements. For example, the apparatus can comprise only two assemblies of one compartment and two conduits, or more than three assemblies. The molten metal is not shown, for convenience of presentation, in FIG. 9.

The second conduits are so designed as to reduce the bulk of this form of apparatus. Each of the second conduits can comprise a portion 56 arranged transversely and a portion 58 debouching into the downstream compartment above or below the level of the molten metal. The axes of each of these two portions, extend downwards at considerable angles with the vertical, about 60 in the case of the portion 56 and about 80 for the portion 58.

The apparatus illustrated comprises three main compartments 60, 62, 64, the metal to be treated being supplied continuously to the compartment 60. The metal passes from these compartments into three first conduits 66, 68 ,70, passing through the second conduits into the following compartments. A final compartment 72 is provided from which the treated melt issues through an orifice 74 situated at the lower portion of a lateral wall. This orifice can be replaced by a bottom orifice closed by a stopper rod.

A gas which serves to cause the metal to flow from one compartment to the following is injected through porous, gas permeable, members 76, 7 8, 80 arranged below the first conduits. A gas required for completing the treatment, which canbe an inert or reactive gas, and which can contain a powder, for example for modulation, can 'be injected through nozzles 82, 84, 86 which, like the nozzles illustrated in FIGS. 3 to 6, are tubes cooled by a water jacket. The nozzles can also be used for the injection of liquids.

Since the rate of supply of molten metal to the compartment '60 and, therefore, the quantity of metal discharged, is fixed, the levels in the compartments, other than the compartment 72 where this is not important, are easily controlled by the gas flow rates through the porous members.

The apparatus described above can be modified without departing from the scope of the present invention. For example, it is possible to provide several porous, gas permeable, members at the lower portion of the single, orthe first, conduit. The porous members can be replaced by injection nozzles, although the results obtained with the same quantity of injection gas are less satisfactory. Means for additional supply of gas can be provided in the single, or the first, conduit at a higher level than that provided at the lower portion thereof. Covers may be used to cover all or part of the apparatus.

In the case of the apparatus shown in FIGS. 7 to 9, incompletely treated metal can be discharged through an orifice provided, for example, in the bottom of one of the compartments 62, 64. When refining pig iron using oxygen, pig iron having, for example, a low carbon conterit or steel having a desired carbon can be discharged from compartment '62 or 64, extra-mild steel being discharged at the outlet of the compartment 72.

Orifices can be provided towards the upper portion of the ladles or compartments in order to allow removal of the slags which form.

The second conduit of an apparatus of the type shown in FIGS. 3, 4, 7, 8, '9 can be so designed that the treated metal pours into the compartment which follows it at any desired height in relation to the level of metal in this compartment.

The second conduit, when present, or at least those portions thereof which are most subjected to corrosion, can be formed by an element which is readily replaced.

The overall shape of the ladles or compartments can be varied from that illustrated. For example, in the case of FIGS. 5 and 6, the ladles can be elongated, as seen in plan view, i.e. elliptical in cross-section in order that the second conduit can be lengthened, or in order that two pairs of first and second conduits can be provided.

The following examples illustrate the process of the invention:

EXAMPLE 1 A ladle of the type shown in FIGS. 5 and 6 was employed to dehydrogenate steel. It was found that 10 metric tons of steel could be dehydrogenated in 6 minutes when the injection of gas through the gas permeable plate 14 was supplemented by a substantial gas injection through the nozzles 31, 32. The cross-section of the conduit 8 was 0.03 m. the rate of flow of the steel therein was 150 metric tons per hour and the rate of flow of the gas, argon, was 10.8. The area of the upper surface of the porous member 14 was 150 cm. Argon was blown into the metal for degasification purposes through the nozzles 31, 32 at a flow rate of 400 Nm. h.

The depth of the molten metal was 1.3 m. If the first conduit was of sufficient height above the melt in the compartment 10 and there were no pressure losses therein, the gas injection would cause the level of metal to rise to about 0. In. above its surface level in the compartmeht 10, the hydrostatic pressure of the layer 20 not being considered. In general practice, it will only be necessary for the second conduit to rise to about 0.40 m. above the surface level in the compartment 10'. The pressure dilference of 0.40 m. will be taken up by pressure losses.

7 EXAMPLE 2 Example 1 was repeated using a similar, but larger ladle containing 50 metric tons of steel to be treated in 12 minutes. Argon was injected at 18 m. /h. into the bottom of a conduit 8 having a cross-section of 0.125 m. and a further quantity of argon was injected through nozzles 31, 32 at a rate of 1000 Nmfi/h. It was thus possible to lower the hydrogen content of the steel from 5 to 6 cm. per 100 g. to 1.5 to 2 cm. per 100 g.

EXAMPLE 3 The apparatus employed corresponded in its essential details to that shown in FIGS; 7, 8 and 9 of the accompanying drawings. The compartments 60, 62, 64 were 180 cm. in height, had a length (at right angles to the plane of FIG. 7) of 60 cm. and a width (in the plane of FIG. 7) of 50 cm., in the upper region, and 1'8 cm. in the lower region. The first conduits 6 8, 70, 72 had a height of 150 cm. and a diameter of 18 cm. The second conduits 56, 58 had an overall length of about 90 cm. and a diameter of 18 cm. The upper surface of each of the porous members 76, 7 8, 80 was circular having a diameter of cm. The depths of the molten metal, for mean flow rates of molten metal and injected gas supplied through the porous members, were approximately 160 cm. in the compartment '60 and about 125 cm. in each of the compartments 62 and 64. The depth of metal in the compartment 72 varied a great deal with the rate at which metal was discharged prior to taking measurements.

By using this apparatus it was possible to refine pig iron by injecting 15 m. /h. of argon through each of the porous members 76, 78, 80 and injecting 20 mfi/min. of oxygen through each of the tuyeres 82, 84, 86. One metric ton of pig iron was converted into mold steel per minute.

What we claim is:

1. Apparatus for treating molten metal, comprising a container for a bath of molten metal, means laterally confining an upright column of said molten metal of a width substantially less than the width of the bath in said container with said column in communication with said bath at the lower end of said column, and means for introducing bubbles of a gas into the lower end of said column to raise the molten metal in said column, the upper portion of said means laterally confining an upright column of said molten metal being open to the ambient atmosphere whereby the space above the molten metal in said upper portion is at atmospheric pressure.

2. Apparatus as claimed in claim 1, and a conduit communicating with the upper end of said column and at a substantial angle to the vertical, said conduit emptying into a container for molten metal.

3. Apparatus as claimed in claim 2, the container that receives treated metal from said conduit being the firstmentioned container.

4. Apparatus as claimed in claim 2, and means for pneumatically injecting at least one reagent into the metal in said conduit.

5. Apparatus as claimed in claim 2, and means for "blowing an inert gas into the metal in said conduit.

6. Apparatus as claimed in claim 2, comprising at least two said column-confining means and as many said conduits.

7. Apparatus as claimed in claim 1, said means for introducing gas into the lower end of said column comprising a porous gas-permeable member.

8. Apparatus as claimed in claim 7, said porous member being disposed in a wall of said container.

9. Apparatus as claimed in claim 7, said porous member being disposed in the [bottom wall of said container.

10. Apparatus as claimed in claim 1, arranged in series with an apparatus of the same type.

11. Apparatus as claimed in claim 1, said container being open at its top to the ambient atmosphere whereby the space above the bath is at atmospheric pressure.

References Cited UNITED STATES PATENTS 3,019,275 1/ 1962 Lorenz -49 3,042,510 7/1962 Armbruster et al. 75-49 3,050,798 8/1962 Chambers 75-49 3,310,850 3/1967 Armbruster 75-49 3,320,053 5/1967 Lehman 75-49 3,321,300 5/1967 Worner 75-49 3,337,329 8/1967 Finkl 75-49 FOREIGN PATENTS $215,243 4/1968 U.S.S.R. 266-34 T GERALD A. DOST, Primary Examiner US. Cl. X.R. 

